The helicopter, when introduced, was a revolutionary aircraft. With its ability to take off and land vertically, the helicopter was able to accomplish maneuvers that no fixed wing craft could perform. Unfortunately, the aerodynamics of rotating blades impose a limit on helicopter maximum forward speed (apart from drag, motive power and other considerations).
The standard single, tandem or lateral-twin rotor helicopter blades provide lift as well as forward impetus. Even with the addition of independent propulsion from either a propeller or jet engine, the individual blade flight characteristics present the following problem at high speeds. In forward flight, a blade advances into the airstream and then retreats. In high speed forward flight, the retreating blade speed may match the speed of the advancing airstream, producing a zero lift condition. The advancing blade then carries the full lift load, with a destablilizing overturning moment on the craft itself. At speeds below this condition, cyclic pitch control can successfully compensate for the potential instability. There is a tilt-rotor design which solves this problem by directing the forced flow of air in the direction required, by rotating engines and blades altogether. The following is offered as a less complex mechanical solution to this problem.